Ammoniovoltaite, (NH₄)₂Fe²⁺₅Fe³⁺₃Al(SO₄)₁₂(H₂O)₁₈, a new mineral from the Severo-Kambalny geothermal field, Kamchatka, Russia

Abstract

Ammoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18, is a new voltaite-group mineral. The mineral was discovered at the Severo-Kambalny (North-Kambalny) geothermal field, Kambalny volcanic ridge, Southern Kamchatka, Russia. Ammoniovoltaite forms at ~100°C around geothermal gas/steam vents in association with alunogen, tschermigite and pyrite. Crystals of ammoniovoltaite have euhedral habit, are up to 50 µm in size and grow on alunogen plates. Ammoniovoltaite is black with vitreous lustre, opaque, brittle and water-soluble. Neither cleavage nor parting is found, the fracture is conchoidal. The mineral is isotropic, with the refractive index n = 1.602(2) (589 nm). Infrared spectra contain an absorption band at 1433 cm–1 distinctive for the ammonium ion. The chemical composition is (iron content is given in accordance with Mössbauer data, H2O calculated from a crystal-structure refinement, wt.%): FeO 13.26, Fe2O3 11.58, MgO 2.33, ZnO 0.04, Al2O3 2.74, SO3 47.46, K2O 0.19, CaO 0.11, (NH4)2O 2.96, H2O 16.03, total 96.70. The empirical formula based on S = 12 atoms per formula unit is [(NH4)1.88K0.08Ca0.04]Σ2.00(Fe2+3.74Mg1.17Fe3+0.05Zn0.01)Σ4.97(Fe3+2.89Al0.09)Σ2.98Al1.00(SO4)12.00(H2O)18.00. The crystal structure has been refined to R1 = 0.031 and 0.030 on the basis of 1217 and 1462 unique reflections with I >2σ(I) collected at 100 K and room temperature, respectively. Ammoniovoltaite is the ammonium analogue of voltaite. The mineral is cubic, Fd$\bar{3}$c, a = 27.250(1) Å and V = 20234(3) Å3 (at 100 K); and a = 27.322(1) Å and V = 20396(3) Å3 (at RT), with Z = 16. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.67 (74) (022), 7.90 (56) (222), 5.58 (84) (422), 3.560 (100) (731), 3.418 (100) (008) and 2.8660 (37) (931). A brief review of ammonium minerals from various volcanically active geological environments is given.

Crystal-chemistry of sulfates from the Apuan Alps (Tuscany, Italy). VI. Tl-bearing alum-(K) and voltaite from the Fornovolasco mining complex

“…The Fe 3+ doublet shows an isomer shift of 0.46 mm/s and a quadrupole splitting of 0.33 mm/s. These data are in accord with those reported for the synthetic sample Fe 40 Mg 60 of voltaite by Majzlan et al (2013) and for ammoniovoltaite (Zhitova et al 2018). With the assumption of similar recoil-free fractions, the Mössbauer spectrum of voltaite from Fornovolasco indicates an atomic ratio Fe 2+ /Fe tot of 0.55, to be compared with 0.53 and 0.56 calculated for the darker and brighter domains observed in BSE images.…”

Crystal Chemistry and High-Temperature Behaviour of Ammonium Phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O from the Burned Dumps of the Chelyabinsk Coal Basin

“…Ferrierite-NH 4 (NH 4 ,Mg 0.5 ) 5 ( These minerals originate either as fumarolic or mofettic (i.e., "volcanic" minerals) [10,26,30,41] or as secondary phases formed due to the contact with organic matter including burning of coal seams and dumps as well as in guano deposits ( Table 1). The burned dumps of the Chelyabinsk coal basin appeared to be an important locality of ammonium compounds: at least 16 minerals and technogenic mineral-like phases were described there ( Table 2).…”

Efflorescent Sulphates with M+ and M2+ Cations from Fumarole and Active Geothermal Fields of Mutnovsky Volcano (Kamchatka, Russia)

“…The (volcanic) steam bears such main (mineral-forming) chemical elements as N (NH 4 ), Ca, minor Mg, S, O, and H (Table S2) and has a pH of ~5. Oxidation of the discharging fluid occurs on the day surface, so the thermal water from the fields is more acidic with a pH below 3 in most cases (Table S2), and it is enriched by elements such as Na, K, Fe, and Al that, as in the literature [52][53][54], are supposed to come from the leaching of the host rocks. It is interesting that the main elements in the chemical composition of minerals fully correspond to the main elements of thermal water (Tables 1-3, Figure 7).…”